Pressurized sub-cooled cryogenic system and method of use

ABSTRACT

A cryogenic system as well as a method of generating a pressurized, sub-cooled mixed-phase cryogen and a method of delivering such a cryogen to a cryoprobe are disclosed. In an embodiment, the cryogenic system includes a reservoir containing a liquid cryogen and a sub-cooling coil immersed in the liquid cryogen. The cryogen is supplied to the sub-cooling coil and is cooled under pressure to produce a pressurized mixed phase cryogen within the sub-cooling coil. This pressurized mixed phase cryogen is provided via supply line to a cryo-device for use.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of co-pending U.S. ProvisionalPatent Application No. 61/980,396, filed Apr. 16, 2014, which is herebyincorporated herein as though fully set forth.

BACKGROUND OF THE INVENTION

The invention relates generally to cryogenic medical devices. Moreparticularly, the invention relates to a cryogenic medical device fordelivering a pressurized sub-cooled, mix-phased cryogen to a cryoprobe.

With the strong movement in the medical community toward the use ofminimally invasive therapies, ablation therapies are becoming moreprevalent. Cryotherapy (or cryoablation) is a minimally invasive methodof treating disease by freezing an area to ablate a target tissue.Cryotherapy provides an alternative to radical surgery, radiationtherapy, chemotherapy, and hyperthermal ablation. Advantages of ablationtherapies relative to these conventional therapies include, for example,precise eradication of targeted tissue, decreased hospitalization time,limited postoperative morbidities, shortened return interval toactivities of daily living, reduced severity and incidence of sideeffects, and reduced overall treatment cost.

Cryotherapy is currently used to treat numerous disease states includingbut not limited to: benign and cancerous tumors of the prostate, kidney,liver, pancreas, bone, and skin, as well as cardiovascular disease,retinal detachment, pain management, and other illness/disease states.In many applications, it is desirable to be able to selectively freeze avery small area to a very low temperature without affecting thetemperature of surrounding tissues and organs.

Cryogens that have been used for ablation procedures include liquidnitrogen (LN₂), critical nitrogen (CN), supercritical nitrogen (SCN),nitrous oxide (NO), argon gas (Ar), and carbon dioxide (CO₂). Currentsystems and devices have focused on delivery of the liquid cryogenthrough the use of low to moderate pressure (15-450 psi) on the entiresystem, piston/bellows compression to drive fluid movement, creation ofcritical or supercritical states through heat and pressurization(500-1200 psi), or alternatively, the use of cryogen gases such asnitrous oxide, carbon dioxide, and argon under extremely high pressures,e.g., 3,000-6,000 psi in Joule-Thomson based systems. Each of thesesystems has significant drawbacks.

In the case of high pressure, gas cryogen Joule-Thomson based systems,ineffective cooling and limited ability to drive ablative temperatures(e.g., −40° C.) into target tissues is a significant inherent weakness.Further, Joule-Thomson systems rely on the use of costly rare gases suchas argon and nitrous oxide, delivered under high pressures, which limitsthe use of these systems.

Liquid systems, on the other hand, provide colder temperatures andgreater freezing (heat extraction) capacity, but are slow to achieve atarget temperature and often result in over-freezing of tissue. Thisresults in unwanted collateral damage to surrounding tissue. Finally,systems utilizing cryogens in a critical or supercritical state, whileproviding a more powerful and quicker freeze, require complicated devicearchitecture and larger cryogen reservoirs, and face challenges in theability to run multiple probes in complex sequences.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides a cryogenic system comprisinga reservoir containing a liquid cryogen, and a sub-cooling coil immersedin the liquid cryogen. A cryogen is supplied to the sub-cooling coil andis cooled within the sub-cooling coil under pressure to produce apressurized mixed phase cryogen. The pressurized mixed phase cryogen isdelivered to the cryo-device by a supply line.

A second aspect of the disclosure provides a method of generating apressurized, mixed-phase, sub-cooled cryogen. The method comprisesproviding a reservoir containing a liquid cryogen and a sub-cooling coilimmersed in the liquid cryogen, the sub-cooling coil having an input endand an output end not immersed in the liquid cryogen; and introducing apressurized gas cryogen to the input end of the sub-cooling coil. Themethod further comprises the steps of cooling the pressurized gascryogen within the sub-cooling coil; and collecting the pressurized gascryogen at an output end of the sub-cooling coil.

A third aspect of the disclosure provides a method of providing apressurized, mixed-phase, sub-cooled cryogen for use in a cryoprobe, themethod comprising the steps of: providing a reservoir containing aliquid cryogen and a sub-cooling coil immersed in the liquid cryogen,the sub-cooling coil having an input end and an output end not immersedin the liquid cryogen; introducing a pressurized gas cryogen to theinput end of the sub-cooling coil; cooling the pressurized gas cryogenwithin the sub-cooling coil to form the pressurized, mixed-phase,sub-cooled cryogen; delivering the pressurized, mixed-phase, sub-cooledcryogen to a tip of the cryoprobe via a supply line; and returning theused pressurized, mixed-phase, sub-cooled cryogen from the tip of thecryoprobe to the reservoir.

These and other aspects, advantages and salient features of theinvention will become apparent from the following detailed description,which, when taken in conjunction with the annexed drawings, where likeparts are designated by like reference characters throughout thedrawings, disclose embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a system in accordance with anembodiment of the invention.

FIG. 2 shows a partial cutaway perspective view of a system inaccordance with an embodiment of the invention.

FIG. 3 shows a side cross section view of a system including an internalreservoir and a pressure cylinder in accordance with an embodiment ofthe invention.

FIG. 4 shows a partial cutaway perspective view of a system inaccordance with an embodiment of the invention.

FIG. 5 shows a top view of a system in accordance with an embodiment ofthe invention.

FIG. 6 shows a partial cutaway perspective view of a cryogenicsub-cooling reservoir and sub-cooling coil in accordance with anembodiment of the invention.

FIG. 7 shows a side view of a sub-cooling coil in accordance with anembodiment of the invention.

FIG. 8 shows a schematic rendering of a system including a cryoprobe andan external pressurized cryogen cylinder in accordance with anembodiment of the invention.

FIGS. 9-10 show a probe tip in accordance with an embodiment of theinvention.

FIG. 11 shows a schematic illustration of the control and monitoringsystem portion of the cryogenic system of, e.g., FIG. 1, in accordancewith an embodiment of the invention.

FIG. 12 shows a schematic illustration of a multi-component system inaccordance with an embodiment of the invention.

It is noted that the drawings of the disclosure are not necessarily toscale. The drawings are intended to depict only typical aspects of thedisclosure, and therefore should not be considered as limiting the scopeof the disclosure. In the drawings, like numbering represents likeelements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention are described below in reference totheir application to the operation of a cryogenic system, shown in FIGS.1-10. Although embodiments of the invention are illustrated relative toa closed loop cryogenic probe with recirculating cryogen fluid, it isunderstood that the teachings are equally applicable to other cryogenicsystem configurations, including those with semi-closed loop cryogencirculation. Further, at least one embodiment of the present inventionis described below in reference to a nominal size and including a set ofnominal dimensions and parameters, including temperature and pressure.However, it should be apparent to those skilled in the art that thepresent invention is likewise applicable to any suitable cryogenicsystem. Further, it should be apparent to those skilled in the art thatthe present invention is likewise applicable to various scales of thenominal size and/or nominal dimensions.

FIG. 1 illustrates a closed-loop cryogenic system 100 in which thepressurized sub-cooled cryogen is delivered to a cryoprobe 200 for useduring a procedure, and is contained in both the supply and returnstages. The cryogenic system 100 includes a system enclosure 102, whichmay include, e.g., sidewalls and top and bottom panels. A sub-coolingreservoir 104, which may be, e.g., a vacuum-insulated dewar, may beprovided within the enclosure 102.

As shown in FIG. 2, the sub-cooling reservoir 104 may include a valvedcryogen supply port 106 for filling the reservoir 104. The fill valve106 connects the reservoir 104 with the sub-cooling reservoir fill line108 (FIG. 4), and controls flow of liquid cryogen into the reservoir 104for reservoir filling during operation. Prior to operation, thecryogenic sub-cooling reservoir 104 may be filled with liquefied gascryogen such as, e.g., liquid nitrogen, argon, oxygen, helium, hydrogen,propane, alcohol, ethylene glycol, propanediol, or other cryogens knownin the art, by a cryogenic fill tank (not shown), which may include oneor more liquid cryogen cylinders, and which would connect to thesub-cooling reservoir fill line 108 prior to the connection of thepressurized gas cylinder. After filling, the reservoir 104 may bedetached from the fill tank, and the reservoir 104 may be closed at thevalved cryogen supply port 106 to form a closed reservoir 104. Thereservoir 104 may be made of, e.g., stainless steel or any othermaterial known for providing a vacuum insulated vessel, or may beinsulated by foam or insulating material.

Once the reservoir 104 has been filled, a pressurized cryogenic gassupply is provided. This may be done in any of a number of ways. In oneexample, a pressurized cryogenic gas supply is connected to the highpressure cryogenic gas input connection 112 as illustrated in FIG. 8,and the system is ready for use. The pressurized cryogenic gas supplymay include one or more pressurized cylinders 114 (external in FIG. 8;internal in FIG. 3) linked together in series or in parallel. In variousembodiments, the pressurized cryogen cylinder(s) 114 may be integratedinto the system enclosure 102 as shown in, e.g., FIG. 3, or may beexternal to the system enclosure 102 as shown in FIG. 8. Someembodiments may contain both an internal and an external pressurizedcryogen gas cylinder 114 simultaneously. Alternatively, with referenceto FIG. 3, a cryogenic gas supply may be connected to the low pressurecryogenic gas input connection 110. The low pressure cryogen gas may bedelivered to the compressor 120 via the low pressure cryogen gas inputconnection 110 from any source including the atmosphere, external gascylinders, gas supply lines within a facility, etc., and the lowpressure cryogen gas may be conducted from input connection 110 tocompressor 120 by compressor input line 111. A compressor gas inputsolenoid 113 and compressor gas input pressure regulator 115 may beprovided along compressor gas input line 111, upstream of compressor120. The compressor gas input solenoid 113 and compressor gas inputpressure regulator 115 function to control the flow and input pressureof the low pressure cryogen gas into the compressor 120. The compressorgas input solenoid 113 can be opened or closed to direct flow of the gascryogen into the compressor 120 as well as prevent backflow (leakage) ofthe compressed cryogen from the system when the compressor 120 is not inuse. The compressor gas input regulator 115 is designed to limit thepressure (maximum or minimum) of the input cryogen gas within the inputpressure specification range of the compressor 120. Compressor 120,which may be provided within the enclosure 102, may be used to compressthe gas to achieve a higher pressure, e.g., nominally between about13.79 MPa and about 41.37 MPa (between about 2,000 and about 6,000 psi);or about 20.69 MPa and about 31.03 MPa (about 3,000 to about 4,500 psi).After being compressed by compressor 120, the pressurized cryogen gasmay be supplied to pressurized cylinder 114 by connection line 117,which may include cryogen gas flow valve 119 and pressure check valve122 in order to prevent back flow of pressurized cryogen gas into thecompressor 120 during and following cryogen gas pressure cylinderpressurization. Pressure cylinder 114 may further be provided with anoutput pressure regulator 121 and a pressure sensor 144. The outputpressure regulator 121 enables control of the pressure of the cryogengas exiting the pressure cylinder 114. For example, the pressure of thecryogenic gas contained within the pressure cylinder will vary duringoperation from about 41.37 MPa (6,000 psi) to about 6.89 MPa (1,000psi). While the pressure within pressure cylinder 114 varies, thepressure cylinder regulator 121 can be set to a constant out pressure,thereby providing for delivery of a constant cryogen flow and pressurerange to the sub-cooling coil 124. The pressure sensor 144 is isutilized to monitor the pressure of the cryogen gas within the pressurecylinder 114 when the system is turned on. This includes duringre-pressurization via the compressor 120, during operation for deliveryof the cryogen through the sub-cooling coil 124 and to the probe 200 aswell as during maintenance, holding, or other such operations. Inanother embodiment, the compressor 120 with or without additionalpressurization cylinders may be contained within a separate satelliteunit to the system to which the system can be connected for rechargingwhen not in use. Further, an integrated pressurized cryogen gas cylinder114 may be refilled and/or re-pressurized by direct connection to anexternal high pressure gas source via the high pressure cryogen gasinput connection 112 (FIG. 3), or by a combination of direct connectionand compressor-based embodiments.

In some embodiments, the system may be pressurized during operation,and/or may include a vent muffler assembly 116 (FIGS. 2, 5) which mayinclude a pressure bleeder valve, coil vent solenoid 131, coil vent line129 (FIGS. 2, 4, 5) and/or muffler. The vent muffler assembly 116 may befluidly coupled to the reservoir 104 by a reservoir vent line 118 (FIGS.2, 4, 5), and may be used to vent the system enclosure 102 to thesurrounding environment to prevent excess pressure buildup duringoperation or from static boil off of the liquid cryogen during non-useperiods.

Referring back to FIG. 2, reservoir 104 may include at least onesub-cooling coil 124 submerged within the internal cavity thereof. Thecoil 124 can be any diameter and be made of any metal or plastic. Forexample, the coils 124 may be made of tubing made from copper, stainlesssteel, titanium, or a variety of plastics, and may be coiled to anoverall coil diameter of about 5.1-25.4 cm (about 2-10 inches), althoughsmaller or larger coils can be used. The internal diameter of the tubingused in the coil can be any dimension depending on the desired systemconfiguration (number of ports, run time of system, dimension of probesused, etc.). While any tubing diameter may be utilized, an example of atypical tubing internal diameter range is about 0.5-3.2 mm (about0.020-0.125 inch), or about 0.76-1.78 mm (about 0.03-0.07 inch).

At an input end, the sub-cooling coil 124 is fluidly connected withcryogen gas input line 126 tubing, which is connected via a cryogen gasinput connection 127 to a pressurized cryogen gas cylinder 114 (FIG. 3).The cryogen gas may be supplied to the sub-cooling coil 124 via eitheran integrated or external cylinder 114 of cryogen gas as previouslydescribed. Any size or pressure cryogen gas cylinder 114 may be used,although in one example, the cylinder may contain nitrogen gas at about16.55 MPa, 31.23 MPa, or 41.37 MPa (about 2,400 psi, 4,500 psi, or 6,000psi) starting pressure. The cryogen gas input line 126 may furtherinclude a pressure regulator 121 (FIG. 3) for adjusting the pressure ofthe incoming cryogen gas delivered to the sub-cooling coil 124. Anexemplary incoming cryogen gas pressure may be nominally between, e.g.,about 6.89-10.34 MPa (about 1,000-1,500 psi), and may particularly beabout 8.96 MPa (about 1,300 psi). For example, once cryogen flow isestablished through the cryoprobe 200 (FIGS. 8-10) during a procedure(about 1-2 minutes), the incoming cryogen pressure may be maintained ormay be decreased to any pressure, e.g., nominally about 3.45-5.17 MPa(about 500-750 psi) to conserve cryogen gas supply and extend cryogengas supply cylinder 114 usage time. In this regard, the incoming cryogengas supply pressure may be increased or decreased at any point of aprocedure as desired in support of a variety of scenarios including inorder to compensate for changes in heat load, conservation of pressure,driving of critical isotherms deeper into a target tissue, creation of alarger or smaller freeze area, to activate and/or deactivate any numberof cryoprobes, etc. Upon depressurization (emptying) of the cryogen gassupply cylinder 114, an additional cylinder(s) can be connected and theprocess can be repeated or any number of cylinders may be connected andoperated individually or in combination with one another.

At an output end of the sub-cooling coil 124, the coil 124 may befluidly connected with a cryogen output line 128 (FIGS. 2, 6), which isconnected via supply line 134 (FIG. 5, 6) to a probe or catheter 200(FIGS. 1, 8-10) via a probe connection port 130 coupling connection(FIGS. 1, 3-5). Although only one sub-cooling coil 124 is shown in thefigures, other embodiments may include any number of sub-cooling coils124 fluidly connected with a pressurized cryogen gas supply and a probeconnection port 130 in similar fashion.

The sub-cooling coil 124 is immersed in the liquid cryogen containedwithin the reservoir 104 as shown in FIG. 2. The liquefied gas cryogenmay be, for example, liquid nitrogen, argon, oxygen, helium, hydrogen,propane, alcohol, ethylene glycol, propanediol, or another cryogen asknown in the art. Regardless of the specific cryogen used, eachpressurized cryogenic gas contained in cylinder 114 and used in thesystem must be matched with an appropriate second cryogen within thecryogenic cooling reservoir 104 to provide an appropriate temperature ofthe pressurized gas such that the sub-cooling process within thesub-cooling coil 124 results in an ultra-cold fluid (gas, liquid, mixedphase) but not a solid, which would result in blockage of flow throughthe sub-cooling coil 124. In another embodiment, an ultra-coldrefrigeration system 186 (FIG. 12) or other means of sub-cooling thesub-cooling reservoir 104 in order to sub cool the gas contained withinthe sub-cooling coil 124 to a desired temperature may be utilized inplace of or in conjunction with a cryogen cooling fluid.

As shown in FIGS. 4-5, a pressurized cryogen/sub-cooling coil gas flowcontrol valve and a pressure regulator assembly 132 control the flow ofthe pressurized cryogen into the sub-cooling coil 124. Pressurizedcryogen gas inbound into the coil may be in the range of about6.89-10.34 MPa (about 1,000-1,500 psi), however a pressure range ofabout 3.45-17.24 MPa (about 500-2,500 psi) or greater can also be used.Once the pressurized cryogen enters the sub-cooling coil 124 and passesthrough the immersed portion of the coil 124, the cryogen is sub-cooledby heat exchange between the gas within the coil 124 and the surroundingliquid cryogen bath in the reservoir 104. The submerged sub-cooling coil124 acts as a heat exchanger in which the outer surface of thesub-cooling coil 124 is in direct contact with the cryogen in thereservoir 104, and the internal surface of the sub-cooling coil 124 isin direct contact with the pressurized cryogenic gas. This results inthe cooling and condensation of the cryogen gas within the inner lumenof the sub-cooling coil 124, thereby creating pressurized sub-cooledmixed phase cryogen (liquid and gas) for delivery to the probe 200(FIGS. 1, 8-10). The mixed phase pressurized cryogen has an increasedability to absorb heat (heat extraction capacity) relative to thecryogen gas that was initially introduced into the sub-cooling coil 124.

In one example, where nitrogen gas is provided to the sub-cooling coil124, the pressurized mixed phase sub-cooled cryogen is referred to aspsN₂. In this example, the liquid nitrogen within the sub-coolingreservoir 104 may be maintained at a temperature of about −196° C. Whenthe pressurized N₂ gas is passed through the sub-cooling coil 124, heatis extracted from the N₂ gas and the cryogen is cooled to between −196°C. and about −150° C. In various further embodiments, the cryogen may becooled to between about −185° C. and about −160° C., or between about−170° C. to −160° C., or below about −160° C. Various other temperatureranges may be applicable where cryogens other than nitrogen are used.

As a result of the creation of the mixed phase cryogen within thesub-cooling coil 124, there is typically a drop in the output pressureof the sub-cooling coil 124. This drop varies depending on inputpressure and volume (flow), and characteristics of sub-cooling coil 124volume (tubing or chamber length and diameter). For example, using anapproximately 6.10 m length of 3.18 mm outer diameter (20 ft. length of0.125 inch outer diameter) copper tubing which is coiled and submergedin a liquid nitrogen (LN₂) bath in reservoir 104, an approximately 1.38MPa (200 psi) pressure drop will result from a nitrogen (N₂) gas inputpressure of 8.96 MPa (1,300 psi). This example results in a coil outputpsN₂ pressure of about 7.58 MPa (1,100 psi) for delivery to thecryoprobe.

The pressurized ultra-cold mixed phase cryogen is then delivered at acontrolled rate from the sub-cooling coil 124 to a probe or catheter200. The cryogen passes from the sub-cooling coil 124 to the cryogenoutput line 128, which leads to a supply line or a plurality of supplylines 134 to probe connection port(s) 130 (FIGS. 1, 3-5, and 8). Asingle sub-cooling coil 124 (FIG. 6) may be connected to one or twoports 130 (FIG. 3) for supporting the operation of one or two probes orcatheters 200, although any number or configuration of coils 124 andports 130 can be supported. Pressurized mixed-phase, sub-cooled cryogenmay then be released through a high pressure cryogen flow solenoid orvalve 136 (FIGS. 4 and 5) for delivery into one or more flexiblecryoprobes 200, shown in FIG. 8, such that the cryogen flows rapidly tothe probe 200 via an umbilical line 202. It is noted that the term“umbilical,” as used herein, is used to refer to any flexible orinflexible tubing used to fluidly couple the probe 200 with probeconnection ports 130 on the system enclosure 102. In variousembodiments, the umbilical line 202 may extend up to about 3 meters(about 10 feet) or more, although any length may be used. Shorterdimensions may be better suited where attached tubing, removable,detachable, or disposable parts are integrated in the design. Cryoprobe200 may also include a probe handle 224 disposed in line between theumbilical line 202 and the probe shaft 218. Probe handle 224 may be usedto hold and operate cryoprobe 200, and may include features such as,e.g., a control button 226. The control button 226 can be configured tocontrol any number of functions including on/off of cryogen flow to theprobe 200, setting/changing or monitoring of cryogen pressure during,prior to and following operation, and setting and monitoring a desiredset point temperature for the probe.

The cryogen flows with minimal heat gain or friction from the enclosureto the distal tip 214 of the probe 200 as a result of the pressure headcreated by the continuous pressurized cryogen gas coming into thesub-cooling coil 124 during operation. At the distal end or tip 214 ofthe probe shaft, the internal tubes, i.e., the supply and return tubes204, 206 respectively, come into contact with the probe outer sheath208, and create a defined region or freeze zone 210 of ultra-coldtemperature to cool and freeze the target tissue region. The catheter orprobe 200 is designed to carry the cryogen under various pressures aswell as at varying temperatures.

In the boiling chamber 212 at the probe tip 214, cryogen pressure dropsdue to the increased volume of the chamber and the outflow restriction.Within the boiling chamber 212, the cryogen interacts with the probe tip214, and heat is absorbed (nucleate boiling) along the inner surface ofthe probe sheath 208 at tip 214. Micro-bubbles of cryogen gas condenseback into a liquid, and the warmed cryogen reverts to pressurized mixedphase cryogen as it exits the probe tip 214 through the return line 206and returns via the umbilical line 202 to the sub-cooling cryogenreservoir 104. It is noted that the supply and return lines 204, 206 maycontinue through umbilical line 202 (FIG. 9) in similar substantiallyconcentric fashion as illustrated in probe 200 in FIG. 10, or mayconvert to being substantially parallel within umbilical line 202.

Once the system is activated and the mixed phase cryogen is created inthe sub-cooling coil 124, the cryogen flow dynamic from the sub-coolingcoil 124 to the probe tip 214 occurs rapidly, typically creating ice onthe outer surface 216 of the probe tip 214 within a few seconds, e.g.,about 2 to about 30 seconds. An ultra-cold probe surface 216 temperatureof, e.g., about −160° C. may be attained within about 30-90 seconds.These time estimates vary depending on the probe, attachmentconfiguration, and heat load to which the probe is exposed. The flow ofcryogen from the sub-cooling coil 124 to the probe tip 214 is controlledby a high pressure cryogenic solenoid valve 136 which is interconnectedbetween the output line 128 of the sub-cooling coil 124 and the probeconnection port 130 (FIGS. 4 and 5), e.g., in line with the supply line134. Once the instruments are in place, the cryosurgical procedure canbe performed with freeze times in ranges of, e.g., about 15 seconds toabout 5 minutes or longer. Upon emptying of the first pressurizedcryogen gas cylinder 114, a second cylinder may be activated allowingthe freezing process to continue or be repeated.

In various embodiments, a variety of structural configurations ofprobes, catheters, and tips may be used, having a variety of sizes,shapes, dimensions, and configurations. Further, the probe or catheterused may be a single use disposable or a multi-use/reusable part capableof being sterilized between individual patient treatments. The freezezone 210 may be created where the internal components of the probecontact the outer sheath 208 at a distal end 214 of the probe 200, suchas a distal end in which the supply line 204 and return line 206 conveneat the freezing zone 210 of the tip 214. In other embodiments, thedistal end of the probe 200 may be needle-like, blunt-tipped, or balloontipped, may include a closed loop, or may be of another probe orcatheter tip design.

In any of these embodiments, the cryogen is circulated from theenclosure 102 to the tip 214 of the probe or catheter 200, and thenreturned to the enclosure 102. The supply line 204 extends to a distanceinto the tip 214 beyond the extension of return line 206 such thatcryogen delivered to the tip circulates within the sealed confines ofthe boiling chamber 212 when the catheter or probe 200 is engaged forthe procedure. The supply line 204 can extend any length or distanceinto the tip 214. The probe and catheter shaft 218 and tip 214 may becomposed of any flexible or rigid material including metallic, plastic,or ceramic compositions. Similarly, a balloon-like structure within thesheath 208 may cause the outer sheath 208 to inflate and deflate forcryogenic procedures.

The return line 206 or outer sheath 208 may be connected to a vacuumpump (not shown) within the enclosure 102 near the compressor 120 toevacuate the probe 200 at any point prior to, during or following aprocedure. A vacuum line 138, which may be within or separate from theprobe connection port 130, may be provided for this purpose, as shown inFIG. 5. A vacuum may be formed within the probe 200 upon sealing thecryoprobe vacuum lumen 220 (FIG. 10) and mechanically drawing a vacuumthrough the vacuum line 138. The vacuum line 138 may connect to its ownvacuum system or may be provided in combination with the vacuum pump ofthe cryosystem.

As noted, the cryogen is returned from the cryoprobe 200 by a returnline 206 which runs through the umbilical line 202 and re-enters thesystem enclosure 102 at a probe connection port 130. The returningcryogen may be used in several different ways. In a first embodiment,illustrated in FIG. 5, the returning cryogen is delivered by the returnline 154 into the sub-cooling reservoir 104, via cryogen return port(s)156. In such a case, the return line 154 is vented into the mainsub-cooling reservoir 104 for collection and reuse to refill/maintainthe sub-cooling reservoir 104. Return of the cryogen to the mainreservoir 104 allows the collected cryogen to extend the operation timeof the system.

In a second possible embodiment, the return line 154 may return thecryogen as bulk fluid into a cryogen gas pressure cylinder 114 (FIG. 3).In such an embodiment, cryogen is collected in the cryogen gas pressurecylinder 114, and when collection is complete, the valve 119 is closed.The cylinder 114 pressurizes to a set pressure via either passive oractive boiling and evaporation of the cryogen within the containedpressure cylinder 114. The cylinder 114 may, e.g., passively pressurizeto a preset pressure which may be, e.g., between 13.79-41.37 MPa(2,000-6,000 psi) nominally. The preset pressure may be controlled by apressure relief valve 123 positioned on the cylinder to preventover-pressurization of the cylinder 114. Once re-pressurization iscomplete, the cylinder is ready for subsequent use.

In a third, semi-closed loop embodiment, the returning cryogen may bepassed through a heat exchanger venting system 140 to warm and evaporatethe cryogen prior to release into the atmosphere, as shown in FIG. 2. Insuch an embodiment, the heat exchanger venting system 140, which mayinclude a fan and heater assembly 158, may be used as a heat exchangerto warm any cryogen vapor that is vented from the system prior toventing, to avoid formation of fog in the environment outside theenclosure 102.

Regardless of which combinations of the foregoing features are employedin a given embodiment, a plurality of valve-controlled ports and sensorsmay be provided for monitoring and electronically controllingtemperatures, pressures, and flow rates of cryogen passing through thesub-cooling unit; as well as for monitoring pressurized cylinderpressure; sub-cooling reservoir liquid cryogen level; pressure, flow andtemperature of the attached probe or catheter; time of operation; andother parameters. Collectively, the valves and controls, includingheaters, sensors, motors, or gauges may be controlled by a control andmonitoring center 160.

As shown in FIG. 11, control and monitoring center 160 may furtherinclude a computing device 162 that includes a software program storedin a memory thereof, which when executed, carries out various controland monitoring functions of the system. Computing device 162 performsprocesses described herein in order to monitor system parameters such astime (e.g., elapsed), temperature, pressure, and fluid flow rates, andto control, adjust, or regulate the system parameters in accordance withuser objectives.

Computing device 162 is shown including a processing unit 164 (e.g., oneor more processors), a memory 166, a storage system 168 (e.g., a storagehierarchy), an input/output (I/O) interface component 170 (e.g., one ormore I/O interfaces and/or devices), and a communications pathway 172.In general, processing unit 164 executes program code, such asmonitoring program 174 and control program 176, which are at leastpartially fixed in memory 166. To this extent, processing unit 164 maycomprise a single processing unit, or be distributed across one or moreprocessing units in one or more locations.

Memory 166 can also include local memory, employed during actualexecution of the program code, bulk storage (storage 168), and/or cachememories (not shown) which provide temporary storage of at least someprogram code in order to reduce the number of times code must beretrieved from bulk storage 168 during execution. As such, memory 166may comprise any known type of data storage and/or transmission media,including magnetic media, optical media, random access memory (RAM),read-only memory (ROM), a data cache, a data object, etc. Moreover,similar to processing unit 164, memory 166 may reside at a singlephysical location, comprising one or more types of data storage, or bedistributed across a plurality of physical systems in various forms,included, but not limited to a primary host site and/or a subscriptionbackup site.

While executing program code, processing component 164 can process data,which can result in reading and/or writing transformed data from/tomemory 166 and/or I/O component 170 for further processing. Pathway 172provides a direct or indirect communications link between each of thecomponents in control and monitoring system 160. I/O interface component214 can comprise one or more human I/O devices, which enable a humanuser 178 to interact with control and monitoring system 160 and/or oneor more communications devices to enable a system user 178 tocommunicate with control and monitoring system 160 using any type ofcommunications link.

To this extent, monitoring program 174 and control program 176 canmanage a set of interfaces (e.g., graphical user interface(s),application program interface, and/or the like) that enable human and/orsystem users 178 to interact with monitoring and control programs 174,176. Further, monitoring program 174 can manage (e.g., store, retrieve,create, manipulate, organize, present, etc.) the data collected duringmonitoring using any solution.

In any event, control and monitoring system 160 can comprise one or moregeneral purpose computing articles of manufacture 162 (e.g., computingdevices) capable of executing program code, such as monitoring andcontrol programs 174,176, installed thereon. As used herein, it isunderstood that “program code” means any collection of instructions, inany language, code or notation, that cause a computing device having aninformation processing capability to perform a particular action eitherdirectly or after any combination of the following: (a) conversion toanother language, code or notation; (b) reproduction in a differentmaterial form; and/or (c) decompression. To this extent, monitoring andcontrol programs 174, 176 can be embodied as any combination of systemsoftware and/or application software. As discussed herein, monitoringprogram 174 enables control and monitoring system 160 to implementmonitoring of operational parameters of cryogenic system 100 or tissueon which system 100 is being used. This may include, e.g., display ofoperational parameters on a display 180. Control program 176 enablescontrol and monitoring system 160 to implement user-initiated orautomatic adjustments to operational parameters, which may be madeeither independently or in dependence upon operational parameters asmonitored by monitoring program 174.

In order to provide data to monitoring program 174, sensors locatedthroughout cryogenic system 100 may monitor operating parameters such aspressure, temperature, and fluid level in the reservoir 104, pressure ofthe cryogen at any point within the cylinder(s) 114, coil(s) 124,probe(s) 200 or reservoir 104, and/or may measure other metrics as maybe desired. The sensors may further monitor and provide feedbackinformation control for various valves and components via the controland monitoring center 160. One example of such feedback control is thatof control of pressurization of one or more components such as thepressurized cryogen gas cylinder(s) 114 to maintain the system withindefined safety ranges of the various components, parts and materialsutilized in the system 100.

One possible example of system monitoring may include use of a reservoirlevel sensor 142 (FIGS. 2, 4-5) to monitor the fill level of the liquidcryogen within the sub-cooling reservoir 104 to assure the sub-coolingcoil 124 is submerged. In another example, pressure sensors 144 (FIG. 3)are utilized on the pressurized gas supply cylinders 114 to assure thatthe incoming cryogen gas pressure is within proper operating ranges. Forinstance, when nitrogen is used as the cryogen, pressurized cryogen gascylinder pressure may be 6.89 MPa (1,000 psi) or greater (typicallybetween about 6.89 MPa (1,000 psi) and about 41.37 MPa (6,000 psi)).Pressure sensors 146 may also be utilized to monitor the incomingpressure to the sub-cooling coil 124 to assure it is within the desiredoperating range. For instance, when nitrogen gas is used, a coil inputpressure of between about 6.89 MPa (1,000 psi) and about 10.34 MPa(1,500 psi) is typically targeted. Coil sensors 125 (FIG. 5) may also belocated on the output line 134 of the sub-cooling coil 124 to monitorcryogen flow, pressure, temperature or other desired parameter.

Various temperature sensors 222 (FIG. 10) may also be utilized withinthe system to monitor temperature of the mixed phase cryogen,sub-cooling reservoir 104, probe tip 214, or at any other location. Inthe probe 200, temperature sensors 222 may be thermocouples, and may beused to monitor probe 200 temperature. A display 180 (FIG. 1) on orcoupled to the enclosure 102 may be used in connection with thetemperature sensors 222 or other sensors (e.g., pressure sensors) todisplay operational parameter readings. Any of the valves 106, 122, 132,136 and sensors 144, 146, 222 may be automated to enable a controlledand consistent operation of the cryogenic system (e.g. computercontrolled operation through the electronically controlled, e.g., bycontrol program 176 (FIG. 11) valves). As such, each of the valves andsensors may be in electrical signal communication with control andmonitoring center 160. For example, temperature sensors 222 in probe200, shown in FIG. 10, may be connected to control and monitoring center160 by wires 182, which may be coupled at the enclosure 102 with probesensor interface connections 184, and within the enclosure to controlcenter 160.

As noted, the mechanical and electrical features of the cryogenic systemmay be substantially contained within an enclosure 102 that allows thesystem to be easily transported. As depicted in FIGS. 1 and 3, theenclosure 102 may include any mobile feature such as wheels 148, handles150 (FIG. 3), and fixtures (or allow placement onto a cart having thesefeatures) so that the system can be transported to and from a treatmentlocation. Further, any above-described device configuration may beconnected to a satellite cryogen gas supply cart which contains anynumber of pressurized cylinders 114 (FIG. 8) for operation. Stillfurther, as shown in FIG. 12, the system may be split into a cryogencart 188 containing a cryogen gas pressurization cylinder(s) 114, thesub-cooling reservoir 104 and submerged sub-cooling coil 124, flowvalves and various other components, which may be connected to aseparate control console 190 via a single or multiple umbilical lines orconnection points enabling cryogen connection 192 and electricalconnection 194 communication between the two units for operation. Inaddition to features previously mentioned, electrical features containedwithin or on the enclosure 102 or console 190 may include, for example,probe and electrical interface connection ports 130, 152 for providingelectrical control of the cryoprobe 200. This may include power on/off,heating/thawing, and movement (deflection/steering) control. Theelectrical interface connection ports 152 shown on an exterior of theenclosure 102 of FIG. 1 may provide a connection between the enclosure102 and probe 200 for supplying electronic communication, andcontrol/monitoring as provided by control and monitoring system 160.

The above-described cryogenic system 100 creates an efficient heattransfer environment that extracts heat from targeted tissue creating aprecise ice region. Return gas/liquid mixture flows back through thereturn tubing and is re-collected in the reservoir, thus allowing forrecycling of the unused cryogen without direct discharge into thesurrounding environment, which is typical of gas based cryoablationsystems.

As used herein, the terms “first,” “second,” and the like, do not denoteany order, quantity, or importance, but rather are used to distinguishone element from another, and the terms “a” and “an” herein do notdenote a limitation of quantity, but rather denote the presence of atleast one of the referenced item. The modifier “about” used inconnection with a quantity is inclusive of the stated value and has themeaning dictated by the context (e.g., includes the degree of errorassociated with measurement of the particular quantity). The suffix“(s)” as used herein is intended to include both the singular and theplural of the term that it modifies, thereby including one or more ofthat term (e.g., the metal(s) includes one or more metals). Rangesdisclosed herein are inclusive and independently combinable (e.g.,ranges of “up to about 25 mm, or, more specifically, about 5 mm to about20 mm,” is inclusive of the endpoints and all intermediate values of theranges of “about 5 mm to about 25 mm,” etc.).

While various embodiments are described herein, it will be appreciatedfrom the specification that various combinations of elements, variationsor improvements therein may be made by those skilled in the art, and arewithin the scope of the invention. In addition, many modifications maybe made to adapt a particular situation or material to the teachings ofthe invention without departing from essential scope thereof. Therefore,it is intended that the invention not be limited to the particularembodiment disclosed as the best mode contemplated for carrying out thisinvention, but that the invention will include all embodiments fallingwithin the scope of the appended claims.

What is claimed is:
 1. A cryogenic system comprising: a reservoircontaining a liquid cryogen; a sub-cooling coil immersed in the liquidcryogen, wherein a cryogen is supplied to the sub-cooling coil and iscooled under pressure to produce a pressurized mixed phase cryogenwithin the sub-cooling coil; and a cryo-device fluidly connected to thesub-cooling coil by a supply line such that the pressurized mixed phasecryogen is delivered to the cryo-device.
 2. The cryogenic system ofclaim 1, further comprising a return line for conducting used cryogenaway from the cryo-device.
 3. The cryogenic system of claim 2, whereinthe return line further conducts the used cryogen into the reservoir forcollection.
 4. The cryogenic system of claim 2, wherein the return linefurther conducts the used cryogen as bulk fluid into a cryogen gaspressure cylinder, wherein the cryogen gas pressure cylinder may be usedas a source for the cryogen supplied to the sub-cooling coil.
 5. Thecryogenic system of claim 2, wherein the return line further conductsthe used cryogen to a heat exchanger venting system to warm andevaporate the cryogen prior to release into the atmosphere.
 6. Thecryogenic system of claim 2, further comprising a boiling chamberdisposed at a distal tip of the cryo-device, wherein the return lineaxially extends a first distance into the boiling chamber, and thesupply line axially extends a second, longer distance into the boilingchamber, such that the supply line terminates nearer to the distal tipof the cryo-device than the return line.
 7. The cryogenic system ofclaim 1, wherein the cryo-device is a cryoprobe.
 8. The cryogenic systemof claim 7, further comprising an enclosure in which the reservoir isdisposed; and wherein the cryoprobe further comprises: an umbilical linecoupled to the enclosure; a probe handle coupled to the umbilical line;and a probe shaft having an outer sheath disposed thereon, the probeshaft extending from the probe handle, wherein the supply line isdisposed within the umbilical, the probe handle, and the probe shaft,placing the cryoprobe in fluid communication with the sub-cooling coilwithin the enclosure.
 9. The cryogenic system of claim 8, furthercomprising a vacuum lumen disposed within the probe shaft, the vacuumlumen being in fluid connection with a vacuum pump disposed within theenclosure.
 10. The cryogenic system of claim 1, further comprising atleast one pressurized gas cryogen supply including: a pressurizedcryogen cylinder for supplying the cryogen to the sub-cooling coil. 11.The cryogenic system of claim 10, wherein the at least one pressurizedgas cryogen supply further comprises: two or more pressurized cryogencylinder linked together in series or in parallel.
 12. The cryogenicsystem of claim 10, further comprising at least one pressurized gascryogen supply including: a low pressure cryogen supply and a compressorfor pressurizing the cryogen.
 13. The cryogenic system of claim 1,wherein the liquid cryogen contained within the reservoir is a liquefiedgas cryogen and is one of: nitrogen, argon, oxygen, helium, hydrogen,propane, ethylene glycol, propanediol, or alcohol.
 14. The cryogenicsystem of claim 1, further comprising: at least one sensor formonitoring one or more of: a pressure of a pressurized crygen or thepressurized mixed phase cryogen, a temperature of a pressurized cryogen,the pressurized mixed phase cryogen, the liquid cryogen contained withinthe reservoir, or a tip of the cryo-device, a flow rate of thepressurized cryogen or the pressurized mixed phase cryogen, or a vesselfluid level in the reservoir or a pressurized cryogen supply.
 15. Thecryogenic system of claim 14, further comprising: a control centerincluding a computer-readable storage medium which, when executed by acomputing device, causes the computing device to carry out: receivingfeedback from the at least one sensor; and based on the feedback,controlling at least one operation parameter of the cryogenic system,the at least one operation parameter including one or more of: thepressure of the pressurized crygen or the pressurized mixed phasecryogen, the temperature of the pressurized cryogen, the pressurizedmixed phase cryogen, the liquid cryogen contained within the reservoir,or the tip of the cryo-device, the flow rate of the pressurized cryogenor the pressurized mixed phase cryogen, or the vessel fluid level in thereservoir or the pressurized cryogen supply.
 16. A method of generatinga pressurized, mixed-phase, sub-cooled cryogen, the method comprising:providing a reservoir containing a liquid cryogen and a sub-cooling coilimmersed in the liquid cryogen, the sub-cooling coil having an input endand an output end not immersed in the liquid cryogen; introducing apressurized gas cryogen to the input end of the sub-cooling coil;cooling the pressurized gas cryogen within the sub-cooling coil; andcollecting the pressurized gas cryogen at an output end of thesub-cooling coil.
 17. The method of claim 16, further comprising: priorto introducing the pressurized gas cryogen to the input end of thesub-cooling coil, compressing the gas cryogen to a desired pressure. 18.A method of providing a pressurized, mixed-phase, sub-cooled cryogen foruse in a cryoprobe, the method comprising: providing a reservoircontaining a liquid cryogen and a sub-cooling coil immersed in theliquid cryogen, the sub-cooling coil having an input end and an outputend not immersed in the liquid cryogen; introducing a pressurized gascryogen to the input end of the sub-cooling coil; cooling thepressurized gas cryogen within the sub-cooling coil to form thepressurized, mixed-phase, sub-cooled cryogen; and delivering thepressurized, mixed-phase, sub-cooled cryogen to a tip of the cryoprobevia a supply line.
 19. The method of claim 18, further comprising:returning the used pressurized, mixed-phase, sub-cooled cryogen from thetip of the cryoprobe to the reservoir.
 20. The method of claim 18,further comprising: prior to introducing the pressurized gas cryogen tothe input end of the sub-cooling coil, compressing the gas cryogen to adesired pressure.